1. Field of the Invention
This invention relates generally to the removal of contaminants from used oil, and more particularly to a method of removing acidic compounds, color, and polynuclear aromatic hydrocarbons, and removing or converting heteroatoms from used oil distillates.
2. Description of the Related Art
It has long been recognized that used motor oils can be recycled by removing the contaminants which accumulate therein during operation of the motor vehicles in which the motor oils are utilized. Recently, the American Society for Testing and Materials (ASTM) has promulgated its Designation: D 6074-99 wherein the ASTM Committee D-2 on Petroleum Products and Lubricants has promulgated standards for re-refined base oils. Included in Designation: D 6074-99 are numerous attributes of base oils, including attributes relating to physical properties, compositional properties, chemical properties, and toxicological properties.
Prior to World War II used motor oil was re-refined using a process involving the addition of sulphuric acid in order to separate the contaminants from the useful hydrocarbon components of used motor oil. Re-refining processes of the type involving the addition of sulphuric acid to used motor oil are no longer used because they result in the generation of large amounts of highly toxic acidic sludge which cannot be disposed of economically. Additionally, such re-refining techniques do not fulfill the requirements of ASTM Designation: D 6074-99.
More recently, used motor oils have been re-refined utilizing a process known as hydrotreating. In accordance with the hydrotreating process, used motor oils are treated with hydrogen under high pressure. Hydrotreating is successful in removing olefins and alkanes from used motor oils and can also be used in removing heteroatoms therefrom. However, the hydrotreating process is expensive to the point that it cannot be operated profitably.
U.S. Pat. No. 5,814,207 discloses a used motor oil re-refining method and apparatus wherein up to four evaporators are connected one to another in a series. It will therefore be understood that the apparatus of the '207 patent is expensive to install and use. More importantly, the used motor oil re-refining method of the '207 patent cannot meet the requirements of ASTM Designation: D 6074-99 because it cannot remove heteroatoms and because it cannot meet the toxicological requirements of the designation.
Co-pending U.S. application Ser. No. 09/250,741 filed Feb. 16, 1999, and assigned to the assignee hereof discloses a re-refining process wherein used motor oil is treated with an organic or inorganic base in the presence of a phase transfer catalyst. The process is successful in removing acidic compounds, color, and polynuclear aromatic hydrocarbons and in removing or substituting heteroatoms from used motor oil distillates. Co-pending U.S. application Ser. No. 09/265,903 filed Mar. 24, 1999, and also assigned to the assignee hereof discloses a re-refining process wherein used motor oil is contacted with a highly polar organic solvent, such as N,N-dimethylformamide. The process is successful in removing polynuclear aromatic hydrocarbons, sulphur-containing substances, nitrogen-containing substances, and other contaminants from used motor oil and distillates. The present invention comprises a process for re-refining used motor oils which is an improvement over the process of application Ser. No. 09/250,741. The process of the invention is unique in that it is the only known process which safely and economically fulfills all of the requirements of ASTM Designation: D 6074-99.